MuleSoft Interview Questions for Experienced

If you are a experienced Mule resource and want to appear in a MuleSoft interview then the following interview questions are must to know. Below is a comprehensive set of MuleSoft interview questions and answers which can help in passing the interview. If a fresher is just able to digest these MuleSoft interview questions and answers then i am pretty much sure that he can crack the interview.

These interview questions and answers are beneficial for the interview taker as well, who want to gauge the depth of understanding a candidate have regarding MuleSoft.

1. What do you mean by Flow in Mule?

A flow is the sequence of the message processors. In a flow, we combine multiple processors to handle a message’s receipt, processing, and routing.

2. What is Subflow in a mule?

Subflows are scopes using which you can group event processors, like main flows. However, they lack event sources and error handling scope. A subflow improves the application performance.

3. What is the difference between a flow and a subflow?

FLOW	SUB FLOW
It has a strategy for exception handling	It gets strategy for exception handling
sources that trigger execution exists, like HTTP	no event sources exist to trigger execution
less efficient to reference a flow	referencing a flow shows a good performance

4. What are the Flow Processing Strategies?

1. Synchronous Flow Processing Strategy
2. Queued Flow Processing Strategy
3. Asynchronous Flow Processing Strategy
4. Thread Per Processor Processing Strategy
5. Queued Asynchronous Flow Processing Strategy
6. Non-blocking Flow Processing Strategy
7. Custom Processing Strategy

4. What is a Mule transformer?

Mule transformers prepare a message by altering its contents. You can use a prebuilt transformer for data conversion. For example, you can use an XML-to-Object transformer to convert an XML message to a Java object.

5. What are the advantages of MuleSoft?

Advantages of MuleSoft:

1. It is lightweight but highly scalable
2. MuleSoft can change effortlessly
3. It is a vendor-neutral solution
4. Reusable application components

6. What are the available resources used for modularizing configuration in Mule?

The following resources are available for modularizing configurations in Mule:

1. Independent configuration
2. Inherited configuration
3. Imported Configuration
4. Heterogeneous Configuration

7. How are the messages in Mule composed?

A message in Mule has four different parts:

1. Payload: The main context
2. Properties: The meta information
3. Multiple Name Attachments: Used for multipart messages
4. Exceptional Payload: Holds error

8. What are the configuration patterns provided by MuleSoft?

Configuration patterns make things easier to use. You have the following configuration patterns in MuleSoft:

1. Bridge
2. Validator
3. WS Proxy
4. Simple Service Pattern
5. HTTP Proxy

9. What is the use of Filter in Mule?

Filters help in making smart decisions for message delivery. Filters give sight to the router by analyzing a message. The filter expressions can be true or false. If true, the value gets stored in the output array; otherwise, the program discards it. 

10. What is a Mule Data Integrator?

The Mule Data Integrator is a data visualization mapping tool that provides drag-and-drop features to create code. It solves moving, transforming, and consolidating information from various parts of the enterprise. 

11. What do you mean by SOAP, and what are some of the advantages of it?

SOAP is the Simple Object Access Protocol. You use this protocol when exchanging structured information. Its uses are

1. When web service talks with a client
2. When you need a lightweight protocol
3. When you need to interchange data among various applications
4. When you have to work with different programming languages
5. When you don’t want to customise the World Wide Web

12. What are the parameters to configure a scheduler?

The parameters to configure a scheduler are

1. Frequency: how frequently do you want to do something.
2. Start Delay: how later do you want to start the task after setting the scheduler.
3. Time Unit: it specifies the unit of time (hours, seconds, etc.).

13. What do you mean by correlation context?

Mediation primitives use correlation context when they want to pass values from the request message onto the response.

14. What is fan-in?

The number of inputs a logic gate has is the fan-in; physical logic gates with a large fan-in are slower than those with a small fan-in.

15. What is fan-out?

Fan-out is the number of logic gates connected to a driving gate. It is the maximum number possible without degrading the normal operation. 

16. Mention the features of a Mule ESB.

Features of a Mule ESB:

1. Simple drag-and-drop design
2. capable of visual data mapping and transformation
3. 100s of pre-built certified connectors
4. Centralized monitoring and administration
5. API management
6. Secure Data Gateway for cloud/on-premise connectivity
7. Web-based management console

17. Mention the basic principles of ESB integration

The basic principles of ESB integration are:

1. Orchestration: Synchronizing two or more services
2. Transformation: Transforming data to an application-specific format
3. Transportation: Handling transfer protocols
4. Mediation: Multiple interfaces for multiple versions
5. Non-functional Consistency: A mechanism for managing transactions and security

18. What is the Mule Expression Language?

A Mule-specific lightweight language for manipulating the contents of a message. It gives you a standardized method for evaluating expressions in Mule. 

19. List various endpoints in Mule

Various endpoint in Mule are:

1. Source at Host
2. Target at Host
3. Receive from Partners
4. Send to Partners

20. What is the expansion of SDO?

The expansion of SDO is Service Data Object.

21. Mention the different types of exception handling.

Different types of exception handling:

1. Default Exception Handling Strategy
2. Catch Exception Handling Strategy
3. Reference Exception Handling Strategy
4. Choice Exception Handling Strategy
5. Rollback Exception Handling Strategy

22. What are the advantages of an ESB?

Advantages of an ESB:

1. Integration becomes more flexible
2. Management becomes centralized
3. Avoiding custom code for every integration

23. What is the transient context?

Transient context is used when passing qualities between mediation primitives inside the current flow. It could be the request flow or the response flow.

24. What is API?

API stands for Application Programming Interface which helps two programs communicate. 

25. What are the features of API?

Features of modern API:

1. They adhere to standards like HTTPS.
2. They are more of a product than a code.
3. They have more robust security because of adhering to standards.
4. An API has its software development lifecycle. 

26. What is Payload in MuleSoft?

The payload in MuleSoft is the content of the message. It changes as it travels in the flow. The message processors will enhance it, transform it, extract information from it, or store it to create a new payload. 

27. What are the features of MUnit?

Features of Mule MUnit:

1. Design and test Mule applications and APIs
2. Integrate testing into CI/CD process
3. Autogenerated Tests
4. Make testing more efficient through the CI process 

28. What is a Scatter-Gather router?

The Scatter-Gather router processes a Mule event through different parallel processing routes. You can use it to multicast a single message to several routes and identify which route causes problems. 

29. What is a choice router?

In the choice router, the message gets routed according to DataWeave expressions that evaluate the content. Each expression has different routing options.

30. What are the advantages of the Logger Component?

The logger component logs error messages, status notifications, payloads, etc. It helps you:

1. monitor Mule applications
2.  debug Mule applications

31. List various the categories of Mule Processors

Categories of Mule processors:

1. Connectors
2. Components
3. Filters
4. Routers
5. Scopes
6. Transformers
7. Exception Strategies
8. Business Events

32. What is RAML?

RAML stands for RESTful API Modeling Language; it helps you manage the API lifecycle. It is concise and reusable. 

33. How to achieve the parallel processing in MuleSoft?

To achieve the parallel processing you can use scatter gather or batch job and with mule 42 on wards there is also parallel for each has been added to process the message simultaneously, Please visit scatter gather and parallel for each urls for more information

34. How to invoke the Custom Java Class from inside a DataWeave?

%dw 2.0Import java!com.mycompany::classnameoutput application/json---{  a: classname::methodName("myString")}

35. How to access secure property inside DataWeave?

By using p(‘secure::<property name>’) you can access the secure property defined as part of secure property file in mule application

36. How can you raise error explicitly in Mule flow/subflow?

By using the Raise Error component you can explicitly raise the error in between the flow 

37. How can you handle errors in middle of the processing in MuleSoft?

You can use the Try block to handle the errors in between the flows, try block also support the transaction. By using try block you can use the on-error continue or on-error propagate to handle the error more information

38. How to call Flow from inside a DataWeave?

You can use DataWeave lookup function to call flow from inside a DataWeave It works in Mule apps that are running on Mule Runtime version 4.1.4 and later It takes the flow’s name and an input payload as parameters. For example, lookup(“flowname”, payload)

39. What is the difference between map, mapObject and pluck?

• map is used to iterate over array
• mapObject is used to iterate over object and return object
• pluck iterates over an object and returns an array of keys, values, or indices in that object.

40. How will you combine 2 arrays into single array in MuleSoft?

You can use flatten DataWeave function to combine two arrays in to single array

41. What are target variable in MuleSoft

When creating a flow in mule app, you can store data in variable so that any component in a flow can use it. In Mule 4 Target Variable replaces the Message Enricher of Mule 3, target variable is available with most of the connectors

42. How many phases are there for batch job in Mule 4?

Each batch job contains 3 different Phase

• Load and Dispatch.
• Process
• On Complete.

43. When we should use batch processing?

You can use batch processing when:

• Synchronizing data sets between business applications, such as syncing contacts between two different ERPs
• Extracting, transforming and loading (ETL) information into a target system, such as uploading data from a flat file (CSV) to Hadoop.
• Handling large quantities of incoming data from an API into a different systems

44. Why we use Batch Aggregator scope?

Batch Aggregator scope is used to accumulate a subset of records from a batch step and process them to external source or service for example rather than processing single record to target system you can use batch aggregate to process all the records at once. You can also configure batch aggregator scope to process fixed size groups of records inside a batch aggregator scope

45. What is the difference between For each and Batch Process?

For each do the processing in single thread while Batch Process performs multi-threaded processing

46. How to manage the Transaction in MuleSoft?

MuleSoft supports two types of transactions

• Single resource( Local)
• XA transactions (extended architecture)

You can configure the transaction depends on the requirement

You can start a transaction from a message source. In this case, the entire flow takes part in transaction This is useful when working with messaging connectors to prevent the consumption of the message if a problem occurs when processing it, allowing you to retry later (because of the rollback).

You can also use the Try block which support the transaction when you want to handle the transaction in middle of the flow

There are below transaction Action define the type of action that operations take regarding transactions

• Always_Begin
• Always_Join
• Begin-or-join
• Join-if-possible
• Indifferent
• None
• Not Supported

47. What are various types of error handling in Mule 4?

Mule 4 has redesigned error handling by introducing the error-handler component, which can contain any number of internal handlers and can route an error to the first one matching it. Such handlers are on-error-continue and on-error-propagate.

48. How can you process message asynchronously in MuleSoft?

You can use the Async Scope to process the message asynchronously.

Async can be used to do the processing in parallel with the main flow, it can be used to process the time consuming operations that does not expect a response back  

49. How can you achieve the Reliability in MuleSoft?

If your application uses a transactional transport such as JMS, VM, DB etc. Reliable messaging is ensured by the built in support of transactions in the transport. Reliable messaging pattern is important when dealing with non-transactional endpoints

50. How can you improve performance of Mule Application in MuleSoft?

There are multiple ways to improve the performance

• Try to save the result and reuse them later
• If processing is expansive do it only once and save result and use them later
• Try to put the validation at start of the flow
• Use Streaming to process data
• Try to process the data asynchronously wherever is possible

51. How can you optimize memory efficiency of the Code in MuleSoft?

• Do not save the Payload in to the flow Variable as it is more memory consuming element
• Do not load unnecessary part of the document
• Use better Database polling for highly concurrent scenarios

52. What is distributed file polling?

In mule 4 distributed file polling is used to poll files in cluster nodes

There are few connectors where this feature is enabled by default

• File Connector
• FTP Connector
• SFTP Connector

You can configure connectors to poll only from primary node @primaryNode Only which ignores the default setting set by mule runtime engine

53. What is caching and why to use it?

Caching is a concept with is used to store frequently used data in the memory, file system or database which saves processing time and load if it would have to be accessed from original source location every time.

53. How will you implement caching in MuleSoft?

There are 2 ways to implement the caching in MuleSoft

• Use Object Store
• Use Cache scope to cache the Response

53. What is Mule Cache Scope and what are its storage types?

Caching in Mule ESB can be done by Mule Cache Scope. Mule Cache Scope has 3 storage types –

In-memory: This store the data inside system memory. The data stored with In-memory is non-persistent which means in case of API restart or crash, the data been cached will be lost.

Configuration Properties:

• Store Name
• Maximum number of entries
• TTL (Time to live)
• Expiration Interval

Managed-store: This stores the data in a place defined by ListableObjectStore. The data stored with Managed-store is persistent which means in case of API restart or crash, the data been cached will no be lost.

Configuration Properties:

• Store Name
• Maximum number of entries
• TTL (Time to live)
• Expiration Interval
• Persistence (true/false)

Simple-test-file-store: This stores the data in a file. The data stored with Simple-test-file-store configuration is persistent which means in case of API restart or crash, the data been cached will no be lost.

Configuration Properties:

• Store Name
• Maximum number of entries
• TTL (Time to live)
• Expiration Interval
• Persistence (true/false)
• Name and location of the file

54. If we wanted to process only one message at a time in mule flow how can we achieve that?

we can make a flow to process in single thread, there is an option to define the Max Concurrency  you can configure the same as 1 to   process only one message at a time

As now you have learned the advanced MuleSoft interview questions and answers, now its time to get a deep dive into some other aspects of MuleSoft like DataWeave and AnyPoint platform. Following are some useful links.

• MuleSoft Design Centre Interview Questions
• MuleSoft API Manager Interview Questions
• MuleSoft Anypoint Platform Interview Questions
• MuleSoft Interview Questions for Freshers
• MuleSoft Job Seekers Resources